Thermal battery and method of making the same having solid complex of SO2 and lithium tetrachloroaluminate as electrolyte

ABSTRACT

A light weight, thermal battery having a cathode, an anode and a solid complex of SO 2  and lithium tetrachloroaluminate as the solid electrolyte therein. The solid complex of SO 2  and lithium tetrachloroaluminate is represented by the formula LiAlCl 4 ·xSO 2 , wherein 1.0&lt;x&lt;4. The thermal battery is activated by heating the battery to temperatures of approximately between 35° C. to 90° C. A method of making the thermal battery is taught.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used and licensed byor for the U.S. Government without the payment of any royalty thereon.

FIELD OF THE INVENTION

The present invention relates, in general, to a storage stable, primaryor secondary, light weight, thermal battery that is heat activated byheating the battery to only approximately between 35° C. to 90° C. Moreparticularly, the present invention relates to a thermal battery thatemploys a complex of sulfur dioxide and lithium tetrachloroaluminate asthe electrolyte. Once heat activated, the thermal battery can remainactive until it is completely discharged. No additional heating isneeded. Moreover, the thermal battery of the present invention, onceheat activated can be used at ambient and sub-ambient temperatures. Amethod of making the thermal battery is disclosed.

BACKGROUND OF THE INVENTION

Thermal batteries generally contain an active metal anode, a cathode andan electrolyte that is solid at normal, ambient temperatures. A currentthermal battery, for instance, may comprise a lithium or lithium alloyanode, an FeS₂ cathode and a LiCl/KCl eutectic mixture electrolyte.Because thermal batteries employ an electrolyte that is solid at normal,ambient temperatures, storability of the battery at ambient temperaturesis excellent due to the slow kinetics of the solid to solid reactionbetween the solid electrolyte and the electrodes as well as theinertness of the electrolyte. At normal ambient temperatures, the solidelectrolyte provides very high electrical resistivity allowing nocurrent to pass.

When power is needed, thermal batteries are activated by use of apyrotechnic heat source to rapidly heat and melt the solid electrolyteto a highly conductive liquid. In order to activate these types ofbatteries, conventional, pyrotechnic heat sources must generally heatthe solid electrolyte to over 450° C. in a time period of often lessthan two (2) seconds. Once activated, if the battery cell can uphold thevery high temperature necessary to maintain the electrolyte in itsmolten state, the batteries could generate power for anywhere from a fewseconds up to complete discharge of the battery.

Because of the high temperature of over 450° C. required to melt thesolid electrolyte, a large amount of pyrotechnic heating materials mustbe used. The need for such great quantities of pyrotechnic heatingmaterials adds significantly to the overall weight and size of thethermal battery. This is undesirable. Ideally, one would like tominimize the size and weight of any power source used.

Moreover, once the thermal battery has been activated, it is often aproblem maintaining the high temperatures needed to keep the electrolytein its molten state until power is no longer needed.

In addition, heating the state of the art thermal batteries to such hightemperatures in order to melt the electrolytes and activate the batteryrequires significant time. The time required to activate prior artthermal batteries is on the order of tens to hundreds of milliseconds.It would be desirable to minimize this activation time.

Accordingly, it is desirable to find a suitable electrolyte for use in athermal battery having a lower melting point than those employed by theprior art thermal batteries; consequently, melting the electrolyte andmaintaining it in its molten state would require lesser quantities ofheating materials. In addition, it is further desirable to provide athermal battery cell the activation of which could be accomplished in alesser amount of time and using lesser amounts of heating materials.

U.S. Pat. No. 4,764,438 (Vaughn et al.) provides a lightweight,thermally activated, solid state, electrochemical power supply whichutilizes a solid alkali metal tetrachloroaluminate electrolyte incombination with a transition metal chloride containing cathode. Thebattery taught is thermally activated at relatively low temperatures ofapproximately 85° C. to 105° C. The battery taught, however, is not athermal battery in accordance with the accepted definition of the term“thermal battery.” The electrolyte in Vaughn et al. does not melt duringthe operation of the battery cell. The cell taught by Vaughn et al. isactivated below the melting point of the electrolyte.

U.S. Pat. No. 4,117,207 (Nardi et al.) teaches a thermal battery whichis activated at a relatively low temperature range of 165° C. to 250° C.Although the temperature taught by Nardi et al. to activate the thermalbattery is lower than that needed to activate other conventional thermalbatteries, it would be desirable to provide a thermal battery that canbe activated at yet even lower temperatures; and hence, require the useof less pyrotechnic heating materials and provide for shorter activationtimes as well.

Nardi et al. further teaches a conventional method of making a thermalbattery, which requires obtaining, and sometimes preparing, each of thecathode, electrolyte and anode materials in pulverized/powder form. Eachof these materials is then separately die pressed layer-by-layer in anapparatus, such as the Carver die to provide a thermal battery wherein asolid electrolyte is sandwiched between a cathode and an anode. Thismethod can be time consuming and complex when one considers the varioussteps that are needed to be employed in preparing the individualcomponent materials and in the pressing of the various component partsto form the final battery product. Vaughn et al. teaches this method aswell as a method for producing the batteries therein.

The present invention provides for a novel and relatively easy methodfor making the thermal batteries within the scope of the invention. Thismethod eliminates the numerous steps needed and employed by the priorart.

There exists a continuing need to develop a thermal battery that issmaller, lighter and more quickly activated than conventional, thermalbatteries. Moreover, there is a continuing need to provide a thermalbattery that can be activated at temperatures significantly lower thanthose employed in the prior art thermal battery art. In addition, thereis a need to maintain the molten state of an electrolyte once meltedafter all pyrotechnic heating materials are exhausted. Being able toaccomplish this and provide a method for making such thermal batteriesin a relatively simple and cost-effective fashion is further desirable.The present invention provides a solution to meet the needs described.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a high energy, light weight, thermalbattery that may be quickly activated at temperatures ranging fromapproximately between 35° C. to 90° C. and a method for making the same.The thermal battery within the scope of the present invention employs acathode, an anode, and a solid electrolyte of the formula LiAlCl₄·xSO₂,wherein 1.0<x<4.

The solid electrolyte used becomes molten at temperatures significantlylower than those temperatures needed to melt the solid electrolytesemployed in prior art thermal batteries. Moreover, the solid electrolyteemployed herein, once melted at temperatures greater than ambienttemperature, freezes at temperatures significantly less than theiroriginal melting point. As a matter of fact, the electrolyte employed,once melted, remains in its molten state at ambient, and evensub-ambient temperatures. This electrolyte is, in essence, a supercooledliquid. Because of the properties of the electrolytes employed withinthe scope of the present invention, the amount of pyrotechnic materialsneeded to activate the thermal battery herein and maintain its activityuntil it is completely discharged is merely the amount needed to bringthe solid electrolyte into its molten state. This amount of pyrotechnicmaterial needed is significantly less than that required in conventionalthermal battery operation.

Accordingly, it is an object of the invention to provide a thermalbattery which can be activated at a much lower temperature thanconventional state of the art thermal batteries.

It is an object of the present invention to provide a thermal batterywhich can be quickly activated by heating the battery to a temperatureof approximately 35° C. to 90° C. so as to melt the solid electrolytetherein.

It is a further object of the present invention to provide a thermalbattery wherein the solid electrolyte therein can be thermally melted attemperatures ranging from approximately 15° C. to 70° C. above normal,ambient temperature.

A further object of the present invention is to provide a thermalbattery that may be activated more rapidly than prior art thermalbatteries since less heating and consequently less heating materials arerequired to activate the battery than required by the prior art.

It is a further object of the invention to provide a thermal batterywherein once the cell electrolyte is brought to its molten state,additional or continuous heating of the electrolyte in order to maintainactivation of the battery and completely discharge the battery is nolonger needed regardless of how slowly the battery is discharged.

Yet another object of the invention is to provide a thermal battery thatonce activated, can be used at ambient and sub-ambient temperatures.

Still another object of the present invention is to provide a lightweight, low temperature thermally activated electrochemical cell havingextended storage shelf life.

An additional object of the invention is to provide a method for makingthermal batteries having these desired properties.

The means to achieve these and other objectives of the present inventionwill be apparent from the following description of the invention andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to FIG. 1.

FIG. 1 illustrates a cross section of a thermal battery within the scopeof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The thermal batteries within the scope of the present invention may beof either the primary or rechargeable class of thermal batteries.Pursuant to the objects set forth above, the present invention providesa high energy, high power source having a cathode, an anode and a solidelectrolyte represented by the formula LiAlCl₄·xSO₂, wherein 1.0<x<4.The thermal batteries herein can be quickly activated thermally bymelting the solid electrolyte therein at temperatures betweenapproximately 15° C. to 70° C. above normal ambient temperature(approximately 35° C. to 90° C.).

A typical thermal battery within the scope of the present invention canbe described with reference to FIG. 1. FIG. 1 is a schematicillustration of the cross section of a thermal battery 20 within thescope of the present invention. The figure illustrates cell/batterycasing 3, having positioned therein cathode 5 and anode 7, between whichis sandwiched solid electrolyte 9. FIG. 1 further illustrates thepresence of conventional heat pellets 11 and 13, which may be employedto activate thermal battery 20.

Cell casing materials, such as nickel or nickel plated cold rolled steelmay be employed as cell/battery casing 3. One having ordinary skill inthe art would be able to select the material best suited to employ asthe cell casing 3 herein. Selection of the casing material, as onehaving skill in the art is aware, largely depends on whether or not thethe casing is connected to the negative electrode.

Cathode 5 may be composed of a porous, high surface area carbon (i.e.Ketjen Black) or a solid cathode material such as CuCl₂, CuCl, CuO(cupric oxide), NiCl₂ or MnO₂, or other, like solid cathode materials.The preferred cathode has a high surface area and may be composed ofKetjen Black, wherein Teflon® is the binder employed.

Anode 7 may be composed of lithium metal or lithium alloyed with othermetals such as aluminum, silicon, tin or like metals.

The solid electrolyte 9 within the scope of the present invention, whichprovides thermal battery 20 with the sought after properties disclosedand is a critical element herein, is a complex of sulfur dioxide andlithium tetrachloroaluminate. This solid complex is represented by theformula LiAlCl₄·xSO₂, wherein 1.0<x<4. The preferred electrolyte is onewherein the value of “x” is 2. A method of producing the electrolytes tobe used within the scope of the present invention is described by Kuo etal., in U.S. Pat. No. 4,891,281, which description is incorporatedherein by reference. The electrolytes produced by Kuo et al., however,are in their liquid state. The sulfur dioxide complexes taught by Kuo etal. are highly conductive, non-pressurized liquids that must be frozenbelow temperatures of approximately −10° C. to be employed as the solidelectrolyte of the thermal battery herein. Conventional methods offreezing may be employed.

The electrolytes employed by the present invention have many desirableproperties for use in thermal batteries and the method of making saidbatteries. These properties can be described as follows:

(1) As mentioned above, when the electrolytes are produced, they areinitially liquid at ambient temperature and must be frozen solid inorder to be employed as an electrolyte in a thermal battery. The liquidform is used in the novel method of making the thermal batteries herein.The method will be described at a later point in this application.

(2) Once frozen solid at temperatures of below −10° C., the solid formof these electrolytes (“solid electrolytes” herein) has melting pointswithin the range of approximately 35° C. to 90° C. The actual meltingpoint of these electrolytes within this range depends on the ratio ofLiAlCl₄ to SO₂ in the electrolyte complex. One having ordinary skill inthe art would be able to determine the desirable ratio of the complex toemploy in order to make a thermal battery having a specific activationtemperature within the above range. The melting points of theseelectrolytes is significantly lower than the melting points ofconventional electrolytes employed in the thermal battery art; and,therefore, lesser amounts of heating materials would be required tobring these electrolytes to their molten state when employed in athermal battery.

(3) Moreover, once these solid electrolytes have been heated to theirmolten state, therefore activating the thermal battery within which theyare employed, the molten complex has the property of supercooling.Stated differently, once molten, the liquid complex has the property ofremaining in its molten state to temperatures well below the temperatureat which it became molten—to temperatures even well below 0° C. Thisproperty allows the thermal battery within which the solid electrolyteherein is employed, once activated, to remain active at ambient, andeven sub-ambient, temperatures.

(4) In addition, in their molten state, these non-pressurizedelectrolytes have very high conductivity in the order of approximately0.1 S/cm at 25° C. and 0.2 S/cm at 60° C. This property permits goodhigh rate discharge performance for a battery within which theelectrolyte is employed.

(5) In their solid state, the electrolytes employed herein are veryresistive, shutting down the battery from discharge, and also providingfavorable storage characteristics to the thermal battery itself. Thesecharacteristics provided to the battery when the electrolyte is in itssolid state is due to the slow solid to solid reaction of theelectrolyte with the electrodes in the battery.

The present invention also relates to a method of making the thermalbatteries herein. The method employed herein does not resemble prior artmethods of making thermal batteries. As discussed in the background,conventional thermal batteries are made by employing thepulverized/powder form of the materials of the various battery componentparts (i.e., anode, cathode, electrolyte) and die pressing eachcomponent individually so as to provide the end product. Because theelectrolytes employed herein are initially liquid at ambient temperaturewhen produced, the complex, multiple-step method of die press need notbe employed herein. Reference to FIG. 1 will be made to describe thenovel method herein.

The thermal battery 20 within the scope of the present invention may bemade in a relatively simple fashion by first positioning a cathode 5 andan anode 7 within cell/battery casing 3 in a conventional fashion. Oncethe cathode 5 and anode 7 have been secured into the casing 3, anelectrolyte 9 within the scope of the present invention in its liquidstate (i.e., either in its liquid state after being initially producedor in its liquid supercooled state), is poured at ambient temperatureinto the case 3 via fill port 15. Once cell casing 3 has been filledwith electrolyte 9 in its liquid state, the cell casing 3 is then sealedin a conventional fashion well within the skill of the art. The cellwith its contents (also referred to as the thermal battery 20) is thenchilled to a specific temperature, for example to below approximately−10° C., in order to freeze the electrolyte 9 therein. The electrolyte9, once frozen solid, will remain in its solid state until the thermalbattery 20 is heated, using heat pellets 11 and 13, to temperaturesabove the melting point of the now solid electrolyte 9 employed. Thismelting point of solid electrolyte 9 is within the temperature range ofapproximately 35° C. to 90° C. Heating the thermal battery 20 to orabove the melting point of electrolyte 9 activates the battery fordischarge.

In the embodiment set forth in FIG. 1, conventional heat pellets 11 and13 are positioned outside the cell/battery casing 3. Any conventionalheating elements/means employed in the thermal battery arts may beemployed herein. Moreover, the conventional heating elements may bepositioned either within the cell/battery casing 3 or external to it.The type of heating elements employed and the positioning of theseconventional heating elements is not critical to the present invention,so long as they operate to provide the essential heating of the solidelectrolyte 9 to initiate discharge of the thermal battery cell 20. Onehaving ordinary skill in the art would be able to select the type andposition of conventional heating elements to employ herein.

Conventional separators (not shown), such as porous membranes ofpolypropylene, may also be employed in the thermal battery 20 to preventthe cathode 5 and anode 7 from coming into contact with one another.

One having ordinary skill in the art will understand from thedescription herein that the thermal battery within the scope of thepresent invention can be activated at a much lower temperature than thatrequired by conventional, state of the art thermal batteries.Consequently, less pyrotechnic, heat source material is required foractivation. Since lesser amounts of heat source materials are needed toactivate the thermal battery, the batteries herein are smaller, lighterand can be activated more quickly than conventional thermal batteries.

An additional property of the thermal battery within the scope of thepresent invention is that once the thermal battery has been activated byheating the electrolyte to its molten state, the electrolyte employedherein will not resolidify when it reaches or goes below thattemperature at which it originally started melting. Once in its moltenstate, the electrolyte remains molten at ambient, and even sub-ambient,temperatures. Hence, the thermal battery within the scope of the presentinvention is the first thermal battery that, once activated, can be usedat ambient and sub-ambient temperatures. The electrolyte employed, oncemolten, can be cooled to temperatures below the melting point as asupercooled liquid. Therefore, under most conditions, the entire thermalbattery cell capacity can be utilized once the electrolyte is in itsmolten state if necessary.

The thermal battery cell of the present invention has excellent shelfstability.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention. Therefore, it is intended that the claims herein are toinclude all such obvious changes and modifications as fall within thetrue spirit and scope of this invention.

I claim:
 1. A light weight, thermal battery comprising an anode; acathode; and a solid electrolyte positioned between and in contact withsaid anode and said cathode, wherein said solid electrolyte is a complexof SO₂ and lithium tetrachloroaluminate.
 2. The thermal battery of claim1, wherein said solid electrolyte is represented by the formulaLiAlCl₄·xSO₂, wherein 1.0<x<4.
 3. The thermal battery of claim 2,wherein said solid electrolyte is LiAlCl₄·2SO₂.
 4. The thermal batteryof claim 1, wherein said solid electrolyte has a melting point rangingfrom approximately 35° C. to 90° C.
 5. The thermal battery of claim 1,wherein said anode is composed of lithium or lithium alloyed with ametal selected from the group consisting of aluminum, silicon and tin.6. The thermal battery of claim 1, wherein said cathode is composed of aporous, high surface area carbon, CuCl₂, CuCl, CuO, NiCl₂ or MnO₂ ormixtures thereof.
 7. A method for producing a light-weight, thermalbattery comprising the steps of: providing a thermal battery cell case;positioning within said thermal battery cell case an anode and acathode; filling, at ambient temperature, said thermal battery cellcase, having positioned therein said anode and said cathode, with aliquid electrolyte; sealing said thermal battery cell case havingpositioned therein said anode, said cathode and said liquid electrolyte;and cooling said sealed thermal battery cell case having therein saidanode, cathode and liquid electrolyte to a temperature sufficient tofreeze said liquid electrolyte, wherein said liquid electrolyte is acomplex of SO₂ and lithium tetrachloroaluminate.
 8. The method of claim7, wherein said temperature sufficient to freeze said liquid electrolyteis below approximately −10° C.
 9. The method of claim 7, wherein saidliquid electrolyte is represented by the formula LiAlCl₄·xSO₂, wherein1.0<+<4.
 10. The method of claim 9, wherein said liquid electrolyte isLiAlCl₄·2SO₂.
 11. The method of claim 7, wherein said liquidelectrolyte, once frozen, has a melting point ranging from approximately35° C. to 90° C.
 12. The method of claim 7, wherein said anode iscomposed of lithium or lithium alloyed with a metal selected from thegroup consisting of aluminum, silicon and tin.
 13. The method of claim7, wherein said cathode is composed of a porous, high surface areacarbon, CuCl₂, CuCl, NiCl₂ or MnO₂ or mixtures thereof.
 14. The methodof claim 7, wherein said thermal battery cell case is composed of nickelor nickel plated cold rolled steel.